OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

September 22, 2023

Deputy Assistant Secretary
Directorate of Enforcement Programs
Respirable Crystalline Silica Focused Inspection Initiative in the Engineered Stone Fabrication and Installation Industries

This memorandum establishes a new initiative to conduct enhanced enforcement and compliance assistance efforts in the engineered stone fabrication1 and installation industries. Based on recent studies of silicosis cases and fatalities,2,3 and a review of prior OSHA inspection history, OSHA has identified the following two North American Industry Classification System (NAICS) codes for this focused initiative: 327991 - Cut Stone and Stone Product Manufacturing, and 423320 - Brick, Stone, and Related Construction Material Merchant Wholesalers. A primary goal of this initiative is to prioritize OSHA inspection activity in workplaces where workers are typically exposed to high levels of silica, and to identify hazards and ensure prompt abatement. All inspections in the two NAICS listed above, programmed and unprogrammed, shall cover the hazards associated with exposure to respirable crystalline silica (RCS or silica).

This initiative supplements OSHA's targeted enforcement under CPL 03-00-023, National Emphasis Program – Respirable Crystalline Silica, February 4, 2020 (or the RCS NEP), which includes NAICS code 327991 on the NEP's primary targeting list and NAICS code 423320 on the NEP's supplemental targeting list. This initiative will commence upon issuance of this memo. Inspections opened under this initiative will count toward each Region's two percent annual inspection goal under the RCS NEP.

Background: OSHA and the National Institute for Occupational Safety and Health (NIOSH) have previously identified exposure to silica as a health hazard to workers involved in manufacturing, finishing, and installing natural and manufactured (i.e., man-made, engineered, artificial, or cultured) stone. See the OSHA-NIOSH Joint Hazard Alert (2015), and see OSHA's Final Rule for RCS (81 Fed. Reg. 16286, 3/25/2016).

In addition, the Centers for Disease Control and Prevention (CDC) published a study in its Morbidity and Mortality Weekly Report (MMWR) in 2019, where eighteen cases of silicosis, including two fatalities, were reported among engineered stone fabrication workers in four states. Several patients also had autoimmune disease and latent tuberculosis infection.2 This CDC report noted that as of 2018, there were an estimated 8,694 establishments and 96,366 employees in the stone fabrication industry in the United States, citing data from the Bureau of Labor Statistics (BLS) for NAICS code 327911 (Cut Stone and Stone Product Manufacturing) and NAICS code 423320 (Brick, Stone, and Related Construction Material Merchant Wholesalers).

More recently, JAMA Network published a study on its Internal Medicine page on Silicosis Among Immigrant Engineered Stone (Quartz) Countertop Fabrication Workers in California, July 24, 2023, which described 52 male patients who were diagnosed with silicosis caused by occupational exposure to respirable silica dust from engineered stone. Twenty of the patients had advanced disease (progressive massive fibrosis), 11 were referred for lung transplants, and 10 died. This study noted that exposure to higher silica dust levels can cause silicosis to occur in acute and accelerated forms over shorter periods of time, as observed among many of the patients in the study with a primary occupation of stone countertop fabricator and who regularly worked with engineered stone . Further, this study stated that an estimated 100,000 stone fabricators in the U.S. are at potential risk for silicosis associated with exposure to respirable crystalline silica, citing BLS data.

Workers in the stone countertop industry saw, grind, polish, and drill slabs of natural (mostly granite) and manufactured stone as part of manufacturing, finishing, and installing countertops. The highest silica levels are associated with manufactured countertops, where crystalline silica is mixed with resins, adhesives, and pigments. Depending on the type of stone in question, these countertops may contain over 90% silica. Engineered stone, for example, contains at least 93% silica. Silica content is usually lower in natural stone products. For example, granite can contain up to 45 – 50% silica. Calcium-based stones, on the other hand, which include limestone and certain varieties of marble (e.g., calcite, dolomite, and onyx), contain little or no silica.4

In facilities that manufacture engineered stone, production operators (such as cutters, grinders, and polishers), inspectors (including quality control technicians), and staff who perform maintenance and housekeeping activities may be exposed to hazardous levels of airborne silica- containing dust. Recently a study reported an outbreak of work‐related asthma and silicosis at a facility that manufactures and fabricates chemical‐resistant countertops comprised of sand, epoxy resin, and phthalic anhydride (PA).5 In addition to the risk of silicosis, therefore, artificial stone workers are at risk for developing work-related asthma, especially among workers who are exposed to asthmagens such as PA, and epoxy resins during the manufacturing process.

Scope: This memorandum applies to Federal OSHA inspections in OSHA Regions 1 through 8, which are the regions with the highest concentration of establishments in the targeted industry sectors. Programmed inspections will be prioritized in the following two NAICS codes: 327991 - Cut Stone and Stone Product Manufacturing, and 423320 - Brick, Stone, and Related Construction Material Merchant Wholesalers. OSHA inspection data shows that silica overexposures are found more frequently in the Cut Stone and Stone Product Manufacturing industry, NAICS 327991, but also that inspections in the Brick, Stone, and Related Construction Material Merchant Wholesalers industry, NAICS 423320, were five times less frequent than in NAICS 327991. This initiative targets and addresses the hazards of overexposure to silica in NAICS 327991 and NAICS 423320 and is expected to increase the likelihood of inspecting high-risk tasks. Area Offices will focus enforcement efforts on these two NAICS codes using the targeting and site selection procedures outlined below.

Although not required, Area Offices (AO) or Regional Offices (RO) may develop a Local Emphasis Program (LEP) or Regional Emphasis Program (REP) if Regions determine that such programs are justified after reviewing relevant data (e.g., review of the number of sites in the region) and considering other resource demands. The instructions in this memorandum should be considered in any REP or LEP developed to inspect facilities in the two NAICS covered by this initiative.

State Plan Impact: Because RCS hazards are nationwide, State Plans were required to adopt the RCS NEP or an at least as effective RCS State Emphasis Program. OSHA also encourages State Plan adoption of the instructions provided in this memorandum.

Targeting and Site Selection: The Office of Statistical Analysis (OSA) has added a new Silica – Engineered Stone industry list to the ListGen establishment search application specifically for this initiative. The Silica – Engineered Stone industry list takes priority over the Silica NEP industry list, and it will provide establishment master lists for each Area Office from the two general industry NAICS codes: 327991 – Cut Stone and Stone Product Manufacturing, and 423320 – Brick, Stone, and Related Construction Material Merchant Wholesalers. Random selections must then be made to inspect establishments from these new master lists. The master lists for this initiative will take priority over existing master lists generated under the RCS NEP until the goal (listed below) of this new initiative is met. After the goal is met, Area Offices may return to using their existing master lists from the RCS NEP, and then should skip any establishments previously inspected under this initiative.

As employers participating in cooperative programs may be exempt from programmed inspections, CSHOs should follow the NEP for needed deletions (e.g., SHARP, VPP, etc.).

Goal: This initiative requires each Area Office in Regions 1 through 8 to complete a minimum of five (5) programmed inspections (i.e., targeting sites selected from NAICS 327991 and 423320) of establishments working with engineered stone, within 12 months from the date of this initiative. Regional Offices may use these inspections to count towards achieving their goal of 2 percent of all inspections under the RCS NEP. Regions should increase this initiative's goal based on local knowledge and concentration of facilities per Area Office. For example, if there is a higher concentration of establishments in any of the covered NAICS codes in one geographic area of the Region, inspections should be concentrated in that area, (some area offices may have no inspections) or a regional/local emphasis program may be implemented. CSHOs may expand the scope of other programmed or unprogrammed inspections to address the covered hazards where worksite conditions or other evidence indicates that such hazards may be present in accordance with the FOM. In addition, multiple inspections shall be opened for each employer whose employees are performing the covered processes at one location. See CPL 02-00-124, Multi-Employer Citation Policy, December 10, 1999.

Covered Processes for Programmed Inspections: Workers involved in manufacturing, finishing, and installing manufactured stone countertops are at risk for significant crystalline silica exposure. Facilities in NAICS codes 327991 or 423320 may be selected for inspection under this initiative if they meet one of the following criteria for work processes:

  • 1) Manufacturing and/or finishing engineered or manufactured stone products at the facility. Activities occurring at these facilities include:
    • Cutting, grinding, chipping, sanding, drilling, and polishing engineered or manufactured stone products.
    • Opening bags of ground quartz, moving or mixing bulk raw materials, cleaning and scraping mixers, or cleaning dust collector bag houses.
    • Changing filters on dust collectors.
    • Making the engineered or cultured slabs— involves mixing crystalline silica, resins, and pigments.
    • Operating powered hand tools, such as saws, grinders, and high-speed polishers.
    • Casting department that mixes and heats raw materials including silica sand (which comprises more than 70% of each countertop by weight), epoxy resin, PA (a known respiratory sensitizer), and pigments.
  • 2) Finishing and/or installing engineered or manufactured stone products off-site.

Note: If neither of the above two criteria is met (e.g., if they only work with natural stone materials), proceed with an inspection if the facility is covered under the RCS NEP.

Inspection Procedures: Inspections under this initiative shall follow inspection procedures in CPL-02-00-164, the Field Operations Manual (FOM) (including the presence of employee representatives, e.g., union officials, during all aspects of the inspection); CPL 02-02-080, Inspection Procedures for the Respirable Crystalline Silica Standards, June 25, 2020; CPL 03-00-023, National Emphasis Program – Respirable Crystalline Silica, February 4, 2020; and other directives relevant to the focused industries and other hazards encountered.

At the opening conference, the CSHO will verify the NAICS code and that the employer's processes meet one of the criteria for inspection under this initiative. If it is determined that the employer does not meet any of the covered processes for inspection, but they otherwise fall under the RCS NEP due to other processes that produce worker exposures to RCS, the CSHO shall continue with the inspection. If it is determined that no such processes are present, then the CSHO shall exit the premises without conducting an inspection.

Inspections shall assess compliance with the provisions of the RCS standards, 29 CFR § 1910.1053 and/or 29 CFR § 1926.1153, in accordance with procedures in CPL 02-02-080, Inspection Procedures for the Respirable Crystalline Silica Standards, June 25, 2020. Note that, as explained in CPL 02-02-080, Section IX.A.6, the silica standard (29 CFR § 1910.1053(a)(3)) allows general industry employers to comply with the construction standard (29 CFR § 1926.1153), instead of the general industry and maritime silica standard, in certain circumstances (see the CPL for further details).

The following requirements from the OSHA Silica standards are provided below for convenience:

  • The Action Level (AL) and Permissible Exposure Limit (PEL).
    • AL of 25 μg/m3 as an 8-hour TWA
    • PEL of 50 μg/m3 as an 8-hour TWA
  • Exposure Assessment (29 CFR § 1910.1053(d) and 29 CFR § 1926.1153(d)(2)).
    • Through document review and interviews, CSHOs should verify how employers determine the amount of silica that workers are exposed to, through either the performance option (i.e., any combination of air monitoring data and objective data) or scheduled monitoring option.
    • CSHOs should collect samples if the employer has not assessed exposure, in accordance with procedures in CPL 02-02-080 (see Appendix B).

Note: Employers that fully and properly implement Table 1 do not need to comply with the PEL or exposure assessment provisions.

  • Table 1 – Specified Exposure Control Methods (29 CFR § 1926.1153(c)).
    • Employers choosing to use Table 1 must fully and properly implement the engineering controls, work practices, and respiratory protection for each employee performing a task listed in Table 1 of the construction standard (29 CFR § 1926.1153(c)).
    • CSHOs should observe work and interview employees regarding use and maintenance of controls and respiratory protection, including the amount of time employees perform tasks on Table 1.
  • Regulated Areas (29 CFR § 1910.1053(e)) (General Industry only).
    • Where workers are exposed above the PEL, CSHOs should inquire as to the location of regulated areas and ensure through interviews that the employer demarcates and limits access to any regulated area(s) and requires the use of respirators by workers in those areas.
  • Methods of Compliance (29 CFR § 1910.1053(f) and 29 CFR § 1926.1153(d)(3)).
    • o CSHOs should verify the dust controls and safer work methods employers use to protect workers from silica exposures above the PEL. According to the OSHA and NIOSH Hazard Alert, the following are control options for countertop manufacturing and finishing operations:
      • Using water spraying systems and remote-controlled tools at the impact site where a saw or grinder generates dust.
      • Large bridge or gantry-like saws usually use water sprays and can be remote-controlled for dust control and cooling.
      • Hand-held angle grinders can be modified to deliver water to the point of contact with the stone.
      • Wet-edge milling machines or stone routers can replace dry grinders in shops. They provide a clean edge profile with a diamond wheel.
      • Using hand tools (e.g., drills, masonry saws, grinders) equipped with a shroud and a vacuum with a high efficiency particulate air (HEPA)-filter when wet methods are not practicable.
      • Installing local exhaust ventilation (LEV) systems at fixed locations to capture dust at its point of origin.
      • Using a combination of both water and ventilation controls, if necessary.
      • Using wet sweeping or HEPA-filtered vacuuming instead of dry sweeping or compressed air.
      • Replacing water and air filters as needed in accordance with manufacturer's instructions to control dust.
      • Adjusting water flow as necessary to control dust, following manufacturers' recommendations for water flow rates.
      • Pre-washing stone slabs prior to cutting.
      • Implementing regular and thorough housekeeping procedures for water slurry and settled dust.
      • In high exposure areas, such as where cutting or polishing work generates silica dust, provide HEPA filtered vacuums for cleaning worker clothes and water for hand, face, and hair cleaning.
    • According to the OSHA and NIOSH Hazard Alert, the following are control options for countertop installation operations:
      • Performing as much work as possible under controlled manufacturing conditions (i.e., using LEV) instead of at an enclosed, unventilated installation site, or performing work outdoors or in well-ventilated areas to reduce RCS dust exposure.
      • Using other dust suppression methods (e.g., LEV) during operations where wet methods for dust control may not be practicable, such as on or near finished cabinets, walls, and floors.
      • Using grinding and drilling tools equipped with dust shrouds coupled with LEV and a HEPA filter. Controls can be either tool mounted (drills) or attached to a vacuum system.
      • Using a HEPA-filtered vacuum to clean up dust as soon as practicable.

Note: If installers are not located on-site or are employed elsewhere, ensure their contact information is obtained to conduct interviews. This may entail expanding the inspection or involving multiple employers. See CPL 02-00-124, Multi-Employer Citation Policy, December 10, 1999.

  • Written Exposure Control Plan (ECP) (29 CFR § 1910.1053(f)(2) and 29 CFR § 1926.1153(g))
    • CSHOs should request and review a copy of the employer's written ECP.
    • In construction, the ECP includes the designation of a competent person (29 CFR § 1926.1153(g)(4)). CSHOs should interview the competent person in addition to employees and employee representatives to ensure all aspects of the ECP are implemented and enforced.
  • Respiratory Protection (29 CFR § 1910.1053(g) and 29 CFR § 1926.1153(e))
    • Refer to CPL 02-02-080, Inspection Procedures for the Respirable Crystalline Silica Standards, June 25, 2020, Section IX.H, and CPL 02-00-158, Inspection Procedures for the Respiratory Protection Standard, June 26, 2014.

Note: General industry employers must provide respiratory protection to workers when dust controls and safer work methods cannot limit exposures to the PEL. Employers following the construction standard must provide respiratory protection either:

  • 1) when specified by Table 1; or,
  • 2) when operating under 29 CFR § 1926.1153(d)(3) instead of Table 1 and dust controls and safer work methods cannot limit exposures to the PEL.
  • Housekeeping Practices (29 CFR § 1910.1053(h) and 29 CFR § 1926.1153(f))
    • CSHOs should observe housekeeping practices throughout the onsite inspection and take bulk samples as necessary. Employers must avoid housekeeping practices that expose workers to silica, where effective safe alternatives are available, such as:
      • Wet sweeping or using HEPA-filtered vacuuming instead of dry sweeping or compressed air.
  • Medical Surveillance (29 CFR § 1910.1053(i) and 29 CFR § 1926.1153(h))
    • Employers must offer medical exams—including chest X-rays and lung function tests—every three years to workers exposed at or above the action level for 30 or more days per year in general industry, and to workers who are required to wear a respirator for 30 or more days per year in construction.
    • CSHOs should ensure employers' procedures include the medical examinations and tests required by the standard, and interview employees to ensure they are offered medical surveillance.
    • CSHOs should review the OSHA logs, document any illnesses related to silica and asthma (e.g., lung cancer, autoimmune disease, respiratory illnesses, TB infection, chronic obstructive pulmonary disease, kidney disease), and bring them to the attention of the CSHO's supervisor and/or Office of Occupational Medicine and Nursing (OOMN) if needed.
  • Communication of Hazards (29 CFR § 1910.1053(j) and 29 CFR § 1926.1153(i))
    • CSHOs, through interviews and document review, should ensure that employers trained workers on the health effects of silica exposure, workplace tasks that can expose them to silica, and ways to limit exposure.
    • o CSHOs should also verify that RCS is included in the employer's hazard communication program in accordance with 29 CFR § 1910.1200. In addition to training, workers must have access to labels on silica containers and safety data sheets (SDS). CSHOs should request and review copies of SDSs for materials containing silica. See also CPL 02-02-079, Inspection Procedures for the Hazard Communications Standard (HCS 2012), July 9, 2015.
  • Recordkeeping (29 CFR § 1910.1053(k) and 29 CFR § 1926.1153(j))
    • o Employers must make and maintain accurate records of air monitoring data, objective data, and medical surveillance. CSHOs should review Section IX.L. of CPL 02-02-080, Inspection Procedures for the Respirable Crystalline Silica Standards, June 25, 2020, for a detailed explanation of requirements and inspection procedures.

Other Hazards: In addition to the hazards associated with RCS, and hazards that may be the subject of the programmed or unprogrammed inspection, other hazards (e.g., crushing hazards from unsecured slabs, guarding of grinders, exposure to resins, adhesives and pigments) that may be encountered in engineered stone fabrication and installation include but are not limited to occupational noise; hazardous chemicals; fall hazards; and lockout/tagout hazards (see, e.g., Safety and Health Information Bulletin 08-12-2008, Hazards of Transporting, Unloading, Storing and Handling Granite, Marble and Stone Slabs). As detailed in the FOM, when such additional hazards come to the attention of the compliance officer, where plain-view hazards are identified during the walkaround, or where information obtained from workers or worker representative(s) indicates deficiencies in compliance, the scope of the inspection may be expanded to include those hazards. CSHOs may address the safety hazards or make a referral.

Applicable OSHA Requirements: Some of the OSHA standards that may be applicable to work involving RCS include, but are not limited to, the following:

    • 29 CFR § 1910.1053, Respirable Crystalline Silica.
    • 29 CFR § 1926.1153, Respirable Crystalline Silica (Construction)
    • 29 CFR § 1910.94, Ventilation
    • 29 CFR § 1926.57, Ventilation
    • 29 CFR § 1910.95, Occupational noise exposure
    • 29 CFR § 1910.132, General Requirements-Personal Protective Equipment.
    • 29 CFR § 1910.134, Respiratory Protection.
    • 29 CFR § 1910.1020, Access to Employee Exposure and Medical Records.
    • 29 CFR § 1910.1200, Hazard Communication.
    • 29 CFR Part 1904, Recording and Reporting Occupational Injuries and Illness.

Outreach: OSHA has continually conducted outreach at the National, Regional, and Area Office levels since the issuance of a final rule on respirable crystalline silica, published in the Federal Register on March 25, 2016 (see 81 FR at 16285-16890, Occupational Exposure to Respirable Crystalline Silica; Final Rule). Additionally, extensive outreach was conducted subsequent to issuance of CPL 03-00-023, National Emphasis Program – Respirable Crystalline Silica, February 4, 2020, which required a three-month outreach period prior to initiating inspections. The National Office, Regional Offices, and Area Offices shall continue to conduct nationwide outreach on silica upon issuance of this memorandum, using public announcements and communications to media, stakeholders, and alliances. For outreach to the industries covered by this initiative, please ensure employers are provided with the OSHA and NIOSH Hazard Alert, Worker Exposure to Silica during Countertop Manufacturing, Finishing and Installation (February 2015), which was updated in September, 2023 with current requirements and resources.

Additionally, OSHA identified two other industries, currently targeted by the RCS NEP, that may also work with engineered stone: 238140 - Masonry Contractors, and 337127 - Institutional Furniture Manufacturing. Employers in these industries should also be informed of the updated Hazard Alert during outreach activities. Area Offices are also encouraged to promote the availability of On-Site Consultation services to small business employers. OSHA resources may be of assistance in this outreach effort. A variety of online resources can be accessed through OSHA's public webpage, including the OSHA Crystalline Silica Safety and Health Topics web page. Internal resources for silica are also available on the OSHA intranet.

OSHA Information System: For all inspections under this engineered stone initiative (NAICS 327991 and 423320), follow existing coding instructions in the RCS NEP (i.e., code "RCS-NEP" under the National Emphasis Program field in the OIS). Add any additional codes for related REPs and LEPs in the engineered stone fabrication and installation industry for either Federal or State Plan enforcement activity.

Program Review: Within one year of the start of this initiative, each affected Regional Office shall send the Office of Health Enforcement a review of their enforcement and outreach activities under this initiative, including, but not limited to, whether the targeting efforts were successful at identifying the establishments with high silica exposures, and information about the types and quality of controls implemented.

This policy is effective as of the date of this memorandum and will be ongoing until otherwise directed. If you have questions, please contact the Office of Health Enforcement at (202) 693-2190.





1 Fabrication includes both manufacturing and finishing for purposes of this document.

2 Rose C, Heinzerling A, Patel K, et al. Severe Silicosis in Engineered Stone Fabrication Workers — California, Colorado, Texas, and Washington, 2017–2019. MMWR Morb Mortal Wkly Rep 2019;68:813–818.

3 Fazio, J. C., Gandhi, S. A., Flattery, J., Heinzerling, A., Kamangar, N., Afif, N., Cummings, K. J., & Harrison, R. J. (2023). Silicosis Among Immigrant Engineered Stone (Quartz) Countertop Fabrication Workers in California. JAMA internal medicine, e233295.

4 OSHA and NIOSH, Hazard Alert, Worker Exposure to Silica during Countertop Manufacturing, Finishing and Installation (February 2015).

5 Tustin AW, Kundu‐Orwa S, Lodwick J, Cannon DL, McCarthy RB. An outbreak of work‐related asthma and silicosis at a US countertop manufacturing and fabrication facility. Am J Ind Med. 2022;65(1):12-19.